Design Issues Related to the Intermodal Marine-Rail Interface
M. John Vickerman, Jr. Vickerman• Zachary• Miller Oakland, California
A major modernization program currently taking place at the Port of San Fran· computerized control of the facilities, from in cisco illustrates the considerations and constraints involved in planning a state creasing the speed of container handling to monitor of·the-art intermodal marine facility. Creation of layout alternatives for future ing the condition of various terminal equipment. expansion possibilities was essential for long-term planning; however, special A major modernization program currently taking problems involving railroad and truck access must be resolved before the project design is complete. Impediments to designing modern intermodal marine-rail place at the Port of San Francisco illustrates the facilities include problems such as lack of land for expansion of existing facilities considerations and constraints involved in planning and modification of existing facility requirements to accommodate variations in a state-of-the-art intermodal marine facility. In equipment and operations. Larger capacity container ships are necessitating this paper the planning effort for the Port of San modifications to existing facilities, and existing wharf gantry cranes often need Francisco's modernization program is used as a case expensive moo111cat1ons to accommodate the rargur vessels. I he design process SLUCiy; the intent is to review the approach, sum often involves starting with the long-range possibilities and working back to marize key planning and design parameters, and de determine near-term needs. This method allows for the development of differ scribe lessons learned and impediments to planning ent design scenarios for future expansion and also identifies near-term designs modern intermodal marine-rail facilities. that can be most effectively adapted in the long term.
FACTORS THAT INFLUENCE INTERMODAL CONTAINER Since the emergence of containerized shipping in the TERMINAL PLANNING AND DESIGN PARAMETERS early 1960s, technological developments in vessel and shoreside facilities have had to keep pace with Effec ts of Deregulation a dramatic expansion of U.S. and world trade. U.S. maritime · facilities, particularly Pacific Coast Economic pressures supported by deregulation have ports, have been critical in enabling the United provided the impetus for new innovative and flexible States to maintain world leadership in maritime com containerized services. Intermodal rail traffic was merce, and the U.S. West Coast, specifically the exempted from regulation by the Interstate Commerce maritime complex of the San Francisco Bay Area, is a Commission in March 1981 following the passage of vital element in the nation's transportation system. the Staggers Rail Act of 1980. Deregulation in gen Today, full cellular container vessels, some with eral has fostered keen competition among many trans container storage capacities in excess of 2,500 20-ft portation elements, including railroads, steamship equivalent units (TEUs) and a few with capacities in companies, and truckers. As a result, the intermodal excess of 4,500 TEUs are traversing the world's industry in the United States today is experiencing oceans, entering West Coast ports, and loading or a competitive fire fueled by deregulation and spurred off-loading cargoes in hours. From marine terminals, on by significant marketplace competition. Reports containers are transported across the country to
62 Design Issues 63
Steamship companies have started to take full ad 1. A large metropolitan population base serving vantage of their new-found point-to-point rate-making as a marketi capability, following passage of the 1984 Shipping 2. Geographically well-located suitable harbors Act. Some U.S. steamship lines have been able to and port facilitiesi assemble substantial marketing and operational ad 3. Suitable inland transportation infrastructure vantages made available by this latest deregulation for trucks and railroadsi and legislation. Implementation of a fully intermodal 4. Available support systems such as freight service concept involving water, rail, and road dis forwarders, customhouse brokers, and banks (~). tribution systems is becoming a key ingredient in steamship line strategic and tactical profit pic Currently, major coastal and inland container trans tures. The Shipping Act of 1984 has encouraged fer facilities are being planned for Los Angeles, steamship lines to become more flexible and innova Chicago, and New York, which will reinforce the tive, and with deregulation have come long-term transport terminal center concept. investment decisions that can substantially cut intermodal operating costs (ll . Vessel and Crane Geometry Requirements Thus planners and designers of intermodal facili In an advisory document produced by the Ministry of ties must provide flexible layout concepts and Transport, Government of Japan (~) , the need to designs to accommodate rapidly growing intermodal respond to future increases in container ship size activity and to match capabilities of present and and equipment advances is addressed. This document future facilities with the operating versatility of forecasts the need for water depth alongside modern intermodal companies. container terminal facilities of from 32 to 49 ft. The Port of Tokyo is reportedly planning a water depth next to wharves of 42 ft, and the Port of Kobe Intermodal Service Expansion is reportedly projecting the need for a water depth of 49 ft. Some Japanese authorities are predicting a Deregulation and the surge in intermodalism are fourth generation container ship, possibly offering creating new intermodal, full-service competitors capacities of 5,500 TEU, and apparently Japanese with new operating concepts and new equipment. equipment manufacturers are already gearing up to Steamship lines are becoming the competitors of meet this challenge. truckers and railroads alike, and inland terminals A ship-loading gantry crane servicing the next and ports are competition among themselves to ser generation vessel may have an operating outreach that vice regional hubs and load centers created by such accommodates 16 rows of containers on a ship's deck concerns as Evergreen, u.s. Lines, Sea-Land Service, stacked four high and twelve rows in the hold stacked American President Lines (APL), and Lykes Lines. nine high. This configuration necessitates a gantry In April 1984 APL began its dedicated rail ser crane outreach of from 137 to 141 ft or greater to vice between Los Angeles and Chicago using three service vessels well beyond Panamax class vessel APL-owned container unit trains in a COFC mode. This geometry. High-speed computer-indexed multiple trol service introduced a lightweight, articulated, leys mounted on the outreach boom of the ship-loading double-stacked railroad car. APL, through its newly gantry crane could handle multiple containers at high formed subsidiary AP Intermodal (API), has been able throughput rates. The expected lift capacity for the to secure contracts with railroads that save 25 per fourth generation container gantry crane may be 40 cent of the usual rail freight rate (ll. Recently long tons (6). APL' s operations from Los Angeles to Chicago have Current marine terminal renovation projects that been upgraded to a 250 40-ft equivalent unit (FEU) require deeper drafts can cause significant problems capacity, and APL has significantly expanded its in the modification of existing container wharf involvement in domestic freight transportation by structural systems, especially for a fixed rail forming AP Domestic (APD) , which has acquired three mounted gantry crane oh a pile-supported existing domestic freight brokerage companies. wharf. Widening the wharf deck can be done without The customary three-way relationship among the affecting the stability of the wharf by adding new domestic shipper, the railroads, and the steamship piling and wharf deck to the waterside edge of the company is changing. The domestic shipper now may wharf. However, careful attention must be paid to have an agreement with a steamship company subsidiary the slope stability of underwharf soil embankments such as API or APD and may be billed directly by the when greater water depths are being evaluated at a steamship company !il· marine terminal facility. Wharf widening is fre An outgrowth of these new transportation arrange quently accomplished with underwater sheet piling ments and an influencing factor in planning is the for slope stability, and widenings that are not ac critical concern of the steamship line about the complished by the use of sheet piles may require necessity of transporting empty boxes for return to other retaining devices to stabilize underwater the West Coast (backhaul). With the insertion of slopes. steamship company operations into the domestic Wharf additions can create significant obstruc transport market, containers loaded with domestic tions to vessel maneuvering and berthing constraints cargo are being backhauled. for container ships that frequently have large bul bous bow haul geometries and bow thruster capability. Wharf fendering systems are also greatly affected by these operational concerns. Careful engineering and Transport Terminal Load Center s life-cycle cost analyses must be undertaken for proper facilities modification projects. In addition Although hotly debated, the load center concept is to large initial existing facilities modification gradually being accepted as a standard operational costs, significant cost may be incurred in modifying approach for some steamship lines such as Evergreen an existing crane boom outreach, height, or other and u.s. Lines, which are putting into service crane geometry. round-the-world class vessels with very large con tainer capacities that require improved shoreside Double-Stacked Rail Cars facilities and specialized service operations. Some of the prime factors that are germane to the selec The third generation of double-stacked intermodal tion of load center ports are reported to be rail car is at hand. Lightweight, single-axle, ar- 64 TRB State-of-the-Art Report 4 t iculated platforms have been in existence for the International Containers Limited of Hong Kong. The last 4 or 5 years and are considerably more efficient geometry of the 48-ft box is 9 ft 6 in. (height) by than is the standard 89-ft flatcar. These five-mod B ft 6 in. (width). The purchase calls for 1,400 ule articulated platforms have a container capacity smooth-skinned units for the domestic market and 100 of 10 FEU (10.6 FEU if 45-ft containers are placed exper irnental marine containers incorporating corner on top of 40-ft bottom containers; and have con castings at the 40-ft position to f acilitate handling siderably fewer couplers and more efficient wheels and stacking with conventional container equipment. and brakes. The third generation intermodal car is Frequently, container terminal sites can accommodate specifically designed for COFC traffic. Three manu the 45-ft and even the 48-ft containers by isolating facturers that provide depressed platform or "well" these containers in selected prepositioned yard constructed intermodal cars are Thrall Car Manu areas. Making changes in aisle widths and hostler facturing Co., Pullman Standard Manufacturing, and p athway dimensions may not be required, depending on Gunderson , Inc. • A modern "on-dock" ICTF rail facility capable Immediate construction recommendations also included of accommodating unit train activity to be located filling and leveling pavement that has sustained ma- 66 TRB State-of-the-Art Report 4 FIGURE 1 SFCT project location map. jor settlements of approximately 8 ft; evaluating Port of San Francisco's SFCT South Terminal, encom the feasibility of using a concrete paving block passes the following elements: surface treatment in fill areas; modernizing facility lighting; improving electrical, mechanical and util • Add one additional container terminal facil ity systems; and renovating the existing entrance ity (Berth 92) and renovate and modify two existing facility to alleviate inbound traffic congestion. berths (94 and 96) to provide a modern container Figure 3 shows existing terminal conditions. terminal facil ity. Recommended conceptual plans for the future in • Provide a state-of-the-art ICTF for rail clude the "potential expansion plan" (Figure 4) and operations in close proximity to the SFCT facility the "potential ultimate expansion plan" (Figure 5); utilizing planned track realignments. the latter requires port acquisition of adjacent • Retain the function of Berth 90 as a grain non-port-controlled properties. The potential expan and liquid bulk terminal until implementation of sion plan provides for the addition of a third reno future planned improvements. vated berth by the partial demolition of a transit • Develop an SFCT centralized check-in/check-out shed and the expansion of the backlands to service facility for control of terminal operations. this berth. The potential ultimate expansion plan • Implement an internal traffic circulation system includes the addition of a fourth berth, removal of permitting on-dock access to the ICTF and CFS from all remaining transit sheds, addition of a CFS, ex the container terminals. pansion of existing maintenance buildings, expansion • Provide a new CFS with future expansion of terminal entrance facilities, and expansion of potential in close proximity to the container termi the intermodal rail and truck bridge. nals. Figur es 6 and 7 show the general equipment and wharf section for the recommended project and the As shown in Figures 8 and 9 the projects planned operations plan for the North Terminal. for the South Terminal include • Wharf: A new concrete wharf with all-vertical South Terminal 24-in. prestressed concrete octagonal piles, Pilings are driven into existing subgrade material that is The Southern Waterfront Master Plan of the Port of prepared by using a vertical drain or wick system to San Francisco, for t he init ial development of the increase the strength of the existing subgrade 67 ISLAIS CREEK S A N FRANCISCO B A Y FIGURE 2 SFCT project vicinity map. FIGURE 3 North Terminal, existing conditions. 68 TRB State-of-the-Art Report 4 S,f# Fl?/f#C/SCO 8 /f )" I z •~ • ,1\ _., ... ,.. 9"1ii!iii~ ...... · D.. M.. IN•l .. ··,.... Tu:.:"I~ ' ' ] U"' · · a ..1v1oa 8 •UILOIN• 1.C.T.F. • RIDCJ• /S!/f/S C I? E E !( Cll/f##E! · ~"'"" TYPE: ...... ; . 11·1-1-1 ...... ,.,.,... I tl 9 '"'" iea? Z<>'-' 1oze ...... 1120-•0110<• '"...' ...... , . ~1~4 1:z.o ~ .. I !~It .,,,, 1•'90 ::~:::::: IZH ~-0 lr,00:. 11i.0z. IOB., 11!11! FIGURE 4 Potential expansion plan for North Terminal. material. The wharf includes a walkway and mooring eluding railroad trackage will accommodate land dolphin. Complete utility systems including cathodic bridge rail operations. protection are planned. The wharf includes a modern • Centralized check-in/check-out circulation marine fendering system to accommodate new container road areas: The design includes approximately 16. 45 vessels. acres of roads and entry and parking areas. The en • Backland area: The container yard backland trance requires relocation of the existing lighter area comprises approximately 4 7. 6 acres immediately aboard-ship (LASH) terminal. adjacent to the existing backland area of Berth 94. • Modification of existing berths 94-96: Modi The subgrade is designed to accommodate heavy-duty fications include wheel loads. Initially, a flexible asphalt pavement accommodates a chassis mode of operation with the a. Demolition of the existing Berth 96 container option of increasing asphalt depth to allow greater freight station building. wheel loads in the future. The terminal area includes b. New rail trackage to allow high, wide, and approximately 6.7 acres of bay fill. Complete utility heavy loads access to wharf areas. systems, area lighting, and refrigerated container c. Modification and conversion of the existing storage outlets are included. crane electrification system to a 2400-volt • CFS area: A 52,800 ft' (gross) CFS with system. transfer dock facilities and future expansion cap d . Removal or relocation, or both, of existing abilities will be constructed. reefer outlets from the Berth 94 backland • ICTF: Approximately 33.44 acres of ICTF in- area. 69 SA# FRA#C/SCtl JL 8 ,,; ,Y ••ATH N1 Jl' } I I II• • / S i A / S C R E E I( Cl-IA##Ei •XPAND•D I • .• 1ae1• Ta 1.c.T.PI. I j I I MAXIMUM C:ONTAINER COUNT (TEU I '"""l;l • '" •'lt•t 7-~ _'"[ ~ la .. ... ::%~ .·~ ~ ... 'It;." ..... "'t'r 1+1:i.i ,~ . ,,.,. . ::;·o'~'"° o .~." l ~-- - Z~6 _1!(10 ,,. ...i •:H· ,... ·,;.- 1fU "''" 1}11-"I!" !1~ ~~>_; -- ·'. NORTH :=k41J~ -~~ Z!?~Z ~t~ · lb'i "ls>qo Z7'ffJ l'l, Z01 ti.. G FIGURE 5 Potential ultimate expansion plan for North Terminal. TYPICAL LIGHT STANDARD ~ CHASSIS STORAGE ~ .•.•.•.•.•.•.•.•.•.•.•.•.·.·.·.·~·.·.·~ 300' 69' 74' 74• 74' ~20± ·------__20_9± -r- FACE OF FACE OF II' 11' <:ONCRETE 1,296' CONCRETE WHARF / WHARF N 2296.00 N 1000.00 O' •D' 1DD' 1•a• !liNl!il•il••il!ii~~!iiiiiiiiiiiiiiiil' •CAL•• , ....a·-a .. FIGURE 6 North Terminal general equipment and wharf section. 70 . I· --3~ -ll ( I ••.~ ~: I I 0- ~ I I I => I! I I I I I ' 71 .• • ~ . .• .• !•• •~ gz '- .--- - .~ \ ( \ \ \ 't' \ IL 0 > ( II 72 g. a •• ~ :~; •" l~· u z •:; i ~ c ii= ~ Design Issues 73 e . New wharf fender system compatible with the (before train arrival) to rail car; no tractor re new fender system at Berth 92. quired. • Remote storage outside immediate ICTF using hostlers or road tractors (longer turnaround time). ICTF • Center storage within ICTF using yard hos tlers (short turnaround). The Engineering Feasibility Study for the South Terminal included a determination of the economic The ICTF was planned to accommodate COFC and TOFC and engineering feasibility of an on-dock ICTF. To operations. The master plan postulated the use of meet modern rail operation requirements and the mar two rubber-tired, mobile bridge cranes per working keting guidelines of the port, the ICTF was planned track for lifting containers on and off rail cars to meet the following criteria: and the provision of two runaround tracks. Entry and egress for the ICTF is through one of two gates. An 1. Operation as an on-dock facility. internal terminal check-in/check-out area allows 2. Utilization of existing land to construct an containers to be transferred to the ICTF from the efficient, operational, and long-term intermodal rail container yards by yard hostlers while remaining facility. within the customs secure area. Figure 10 is an 3. Expansion capability to meet projected market artist's conception of the ICTF project. demand for ICTF utilization. 4. Construction of facilities to reduce drayage and transfer costs associated with other rail con tainer movements. ICTF Railroad Access 5. Access via existing rail and truck routes. 6. Efficient circulation patterns within the ICTF Investigations were conducted to evaluate the rail with emphasis on cargo throughput and safety. road infrastructure leading to the port complex in order to determine impacts on future SFCT develop Operation schedules and train frequency will ment. In-depth feasibility studies were conducted to determine actual throughput capability of the ICTF. evaluate tunnel and bridge restrictions and to The most critical operational requirement is to determine the practicality of modifying or recon minimize the number of handlings and movements per structing tunnel clearances to accommodate new container unit. This was envisioned as being accom double-stacked container rail cars and other spe plished with yard hostlers who would bring the con cialized high, wide, and heavy rail car operations. tainers to the facility and position them at the Additional studies were undertaken to evaluate outbound staging area adjacent to the working track. trackage alignment and grade for suitability for If this is not possible, the hostler could then connecting marine and intermodal rail facilities with position the containers in the storage area. The four main-line railroad operations. basic operating methods evaluated for the ICTF were The tight clearances of Tunnels 3 and 4 on the Southern Pacific main-line approach into San Fran • Direct staging, without storage transfer from cisco are well known to Bay Area railroaders. The chassis to rail car, using hostlers and road trac clearance diagrams for both of these tunnels relative tors. to the double-stacked rail car configuration are • Prestaging transfer from prestaged chassis shown in Figure 11. Because double-stacked cars and FIGURE 10 Artist's conception of ICTF project. 74 TRB State-of-the-Art Report 4 -··- - · -~ -- ·· oe OF AA1L. VAIZ IEh f. FIGURE 11 Tunnel clearance diagram, existing conditions. other specialized rail cars will not meet the mini with no further excavation. A new concrete invert, mum clearance requirements for the tunnels, several approximately 1-ft thick with reinforcement, could modification schemes were considered. One scheme be constructed. The rail could then be attached centers around a gauntlet track arrangement, with a directly to the concrete with rail clips. This method third track constructed between the existing two was used successfully in constructing the Bay Area tracks. Installation of signal systems could allow Rapid Transit (BART), a heavy rail rapid transit passage of a single train through the center of the system. However, it was concluded that use of the tunnel, with the central crown of the tunnel provid much heavier rail cars loaded with freight would ing the required clearance. The second scheme in crush the isolation pad on the rail clip and cause volves removing the existing concrete invert and structural damage to the concrete. reconstructing a lower invert (Figure 12). A summary This view was supported by the Southern Pacific of the phased construction approach is shown in Fig Railroad, who confirmed that the commuter train line ure 13. The method proposed for lowering the rail uses rail cars that would cause such damage. (Several elevation was to remove the ballast material down to sections with direct concrete fastening systems were the concrete invert, and demolish the concrete invert tested by the U.S. Department of Transportation on .. ~··· _+1 \- -TUt-Jf..Je.L 4- i .,..oe C?E @AIL. COLP) !' FIGURE 12 Proposed tunnel clearance diagram (after lowering of invert). Design Issues 75 1'-J1"0.~10"- fUN>-111-1- WALL (NP fO" e>Of"H "f"l.JNNIOL<;.) e·r,j ; 'f""!'P IM µ,:)c.1<- C.ONOlf"ION ~,, ~L C-ONOl'rlON I...J:'2e2_g...1f; : ~UV ((;YOO ) :--1?2!"_l;F _f\>(.l "'f)".14 •. jliJv ~il.L !'- ~ (·t.'· ?I~) b,,,m...----;;rn,...'liJill't-",_.....~~ FIGURE 13 Proposed tunnel construction sequence (invert-lowering scheme). the Santa Fe Railway in Kansas during 1972-1973. In 12 to 14 in. (to ensure proper clearances) and plac all cases, the tested section failed after a period ing a 12- to 18-in. reinforced concrete invert. of several days under normal freight traffic.) Panels would be replaced and the track raised on It was decided that realignment of the rail line ballast. through the Hunter's Point shipyard with direct Alternative B involves the use of geotextiles that access to the ICTF would involve extremely high cost allow for quicker, less costly construction and af and other inefficiencies. Reconstructing the tunnels ford better drainage. Tunnel 4 and the southern half with a higher clearance arch was rejected on the of Tunnel 3 are laid on a O. 3 percent grade that basis of economic, operational, safety, and time descends to the south. The northern half of Tunnel 3 constraints. is on a 0.10 percent grade that ascends to the south. The proposed solution to modification of the tun These grades will provide adequate tunnel drainage nels is one of two alternatives, both of which result through the drain pipes. Figure 13 shows the proposed in removal of the existing ballast and the 2-ft-thick construction sequence for the tunnel invert lowering. reinforced concrete invert: • Alternative A: After removing the concrete IMPEDIMENTS TO THE APPLICATION OF CURRENT invert, excavate approximately 1 ft to 2 1/2 ft of INTERMODAL CONTAINER TERMINAL PLANNING AND rock or soil. A new reinforced concrete mat with ap DESIGN TECHNIQUES propriate drainage would provide the base for the new ballast of the rail track. The designer of a modern intermodal marine facility • Alternative B: Remove approximately 1 to 2 ft must consider a multiplicity of factors that chal of earth (after removal of the invert) and recompact lenge a successful planning effort. Installation of the earth. Place a track stabilization geotextile huge paved parking areas; goliath cranes; and a fabric over the subgrade material. (Southern Pacific variety of mobile loaders, gantries, and lifts does is currently using track stabilization fabrics in not automatically ensure efficient container terminal similar tunnel conditions with satisfactory results.) operation. These are often the cause of increases in container terminal throughput costs, and large con To accomplish this work, the double-track main line tainer terminal areas can be a deterrent to efficient would be single tracked during the construction container handling. State-of-the-art design must period. capitalize on modes of operation that move containers When the lowering of the tunnel is completed, the from entry to storage areas to ship or rail loading ballast section in Tunnels 3 and 4 would be renewed. cranes and vice versa as quickly and efficiently as Single-tracking could be accomplished by using pres possible at low capital cost. ent crossover switches. All construction work on the The designer must be sensitive to the need for tunnels sh"uld be undertaken during night hours (7 future changes in terminal configurations. Designs p.m. to 5 a.m.) and weekends to avoid interference must accommodate factors as diverse as changes in with commuter traffic. terminal boundaries, future terminal operator These tunnels were built in 1905-1906, and it is requirements, and advances in modes of operation. believed that there is no reinforcing in the con Lack of design flexibility can create significant struction. The tunnel wall footing should be ex down-line costs for frequent modification to facili cavated an additional 2 ft by excavating a 10-ft ties. section and leaving an undisturbed 10-ft section. Factors as diverse as pavement durability, union After the exposed sections are cast and set up, the work rules, ease of maintenance and upkeep of reefer intervening sections would be opened up and cast. outlets, protection of utilities from traffic damage, Alternative A involves excavating an additional worker safety, and facility security must all receive 76 TRB State-of-the-Art Report 4 appropriate design treatment. Relationships among REFERENCES building structures are vital to proper operation and future expansion. For instance, the orientation l. Intermodalism on the Railroad. Intermodal Trans of a readability canopy must be planned so that out portation Container News, Vol. 20, No. 4, April bound trucks can easily maneuver adjacent to the 1985, pp. 10-27. canopy and yet be close enough to the equipment 2. W.H. Dempsey. U.S. Railroads in Midst of an maintenance garage for necessary tire changes and Intermodal Boom. Intermodal Transportation Con minor repairs, tainer News, Vol. 19, No. 4, April 1984, pp. Existing infrastructure constraints further chal 12-26. lenge the marine facility designer. Lack of suitable 3. Era of Uncertainty for U.S. West Coast Box Ports. track curvature and proper clearance in railroad Port Development International, Vol. l, No. 3, tunnels and bridges such as is currently confronting April 1985, pp. 41-44. the Port of San Francisco is a serious impediment to 4. B, Johnson. APC Expands Intermodal Services. rail service access. Intermodal Transportation Container News, Vol. Cost constraints and unanticipated environmental 20, No. 6, June 1985, pp. 24-29. impacts can er ipple even the best planning effort. 5. Load Centers and Landbridges Move to Center stage. The marine terminal facility owner must ensure suf Intermodal Transportation Container News, Vol. ficient funds for the project, including such things 20, No. 6, June 1985, pp. 12-16. as unforeseen site conditions. The intermodal 6. Japan Shapes Up to the 21st Century and Cranes facilities designer must keep the realities of for the Next Generation. Port Development Inter facility costs in mind and yet plan a facility de national, Vol. l, No. 6/7, July/August 1985. signed to achieve anticipated throughputs and the 7. M.T. Hesterman. Double-Stacking: A Maritime View. flexibility to accommodate the current and future Railway Age, May 1985, pp. 46-48. pressures of fully intermodal service.